SPECTROMETER PROBLEMS
DUCTILE IRON
PROBLEMS
WITH THE
CHEMICAL ANALYSIS
DUCTILE IRON
Ir G HENDERIECKX
GIETECH BV
Ir G.D HENDERIECKX
GIETECH BV
OKTOBER 2009
1
SPECTROMETER PROBLEMS
DUCTILE IRON
CONTENT
1. HOW TO GET THE CORRECT CARBON CONTENT?
2. WHAT IN CASE Mg AND S ARE HIGH?
Ir G.D HENDERIECKX
GIETECH BV
OKTOBER 2009
2
SPECTROMETER PROBLEMS
DUCTILE IRON
1. HOW TO GET THE CORRECT CARBON
CONTENT?
1.1 INTRODUCTION
It is known that it is difficult to analyse the iron metal concerning the carbon content
by a spectrometer. Especially the ones with free graphite are difficult, the white high
alloyed irons (without free graphite) are easier to get a good result.
Where the spectrometer has the requirement to be standardized and calibrated
correctly for the iron involved, the “wet chemical” analysis has the problem that:
1. By taking chips, the metal has lost some carbon and the result will be too
low
2. The analysis is a complex process (weighing several small quantities,
using chemicals…), performed by an operator and the accuracy will not be
very high.
The wet chemical analysis requires white solidified small parts that can be broken off
and used for analyzing in order to get the correct carbon content.
On the other hand, the wet chemical analysis is of no use to the melting operator
because he cannot wait that longtime.
So it is required to find a method that can give a correct carbon content, using the
spectrometer.
Ir G.D HENDERIECKX
GIETECH BV
OKTOBER 2009
3
SPECTROMETER PROBLEMS
DUCTILE IRON
1.2 THERMAL ANALYSIS
The thermal analysis, done with a CE-meter (Carbon Equivalent meter) is based on
the cooling curve. From this cooling curve the CE (Carbon Equivalent) is calculated.
The CE can be calculated exactly by this test, based on the Tl (liquidus temperature)
temperature.
The equipment can also indicate the C and Si content using a formula and supposing
that P is nearly all the time constant and very low.
CE = %C + (%Si + %P) / 3.
Some equipment use another formula:
CEL = %C + %Si / 4 + %P / 2
So the calculation of C and Si is less accurate.
Ir G.D HENDERIECKX
GIETECH BV
OKTOBER 2009
4
SPECTROMETER PROBLEMS
DUCTILE IRON
1.3 COMBINING SPECTROMETER AND THERMAL
ANALYSIS
We know that the thermal analysis has a correct CE value.
We also know that the spectrometer result for Si and P (if properly standardized) is
also very accurate.
We take the CE from the thermal analysis minus one third of the sum of Si and P
(taken from the spectrometer) and then we can calculate the carbon content.
% C = CEthermal analysis – (%Si + %P)spectrometer / 3
This can be done at any time of the melting or metal processing, but should enable
the melting operator to correct the result. For this reason it is done at the end of
melting but before the overheating (Tc to Ttap). At this moment in time, the nodulising
and the inoculation is not yet done.
The required analysis before nodulising and inoculation is known, so the calculated
result (see above) can be compared with the required result.
Take in account that nodulising will increase the silicon content (efficiency about 99
%) and decrease the carbon content (mostly around 0,1 %, but should be checked).
The inoculation is increasing the silicon content with efficiency of about 97 %. These
efficiency figures should be checked in each foundry.
Ir G.D HENDERIECKX
GIETECH BV
OKTOBER 2009
5
SPECTROMETER PROBLEMS
DUCTILE IRON
2. WHAT IN CASE Mg AND S ARE HIGH?
It is sure that the following formula is correct if there are no RE (Rare Earths) used:
Mgadd = (0,76 x Sinitial + Mgresidual) / ƞ
Mgadd: added Mg content, equals % addition of FeSiMg x % Mg in the alloy
Sinitial: % of S in the metal before nodulising
Mgresidual: % of Mg after nodulising (Mg + MgS)
Ƞ:
efficiency of the nodulising process, which is less than 1 because some Mg
escapes the metal without reaction, some by reacting to MgO. If the melting
procedure is stable, this factor also should be stable.
The efficiency of most industrial nodulising processes is around 0,7.
Conclusion:
1. The Sresidual < Sinitial
2. Mgresidualtested < Mgadd x ƞ
3. Mgresidual < Mgadd x ƞ – (Sinitial – Sresidual) x 0,76
If one of the conditions is not met, the testing (chemical analysis) is not correct!
Ir G.D HENDERIECKX
GIETECH BV
OKTOBER 2009
6
SPECTROMETER PROBLEMS
DUCTILE IRON
Examples
Metal with Sinitial = 0,020 %, adding 1,4 % FeSiMg with 7 % of Mg
1. Result is Mgresidual = 0,08 % and Sresidual = 0,017 %
1. 0,017 < 0,020
2. 0,08 < (0,014x0,07/100) x 0,7 = 0,09 x 0,7 = 0,063
3. 0,08 < 0,09 x 0,7 – (0,020 – 0,017) x 0,76 = 0,061
YES
NO
NO
The amount of Mgresidual is too high (see 2), confirmed by the formula
3.
2. Result is Mgresidual = 0,08 % and Sresidual = 0,020 %
1. 0,020 < 0,020
2. 0,08 < (0,014x0,07/100) x 0,7 = 0,09 x 0,7 = 0,063
3. 0,08 < 0,09 x 0,7 – (0,020 – 0,020) x 0,76 = 0,063
NO
NO
NO
The amount of Sresidual (see 1) and Mgresidual (see 2) and formula 3
are too high.
3. Result is Mgresidual = 0,08 % and Sresidual = 0,010 %
1. 0,010 < 0,020
2. 0,08 < (0,014x0,07/100) x 0,7 = 0,09 x 0,7 = 0,063
3. 0,08 < 0,09x 0,7 – (0,020 – 0,010) x 0,76 = 0,0544
YES
NO
NO
The amount of Mgresidual is too high (see 2) as well formula 3.
4. Result is Mgresidual = 0,05 % and Sresidual = 0,017 %
1. 0,017 < 0,020
2. 0,05 < (0,014x0,07/100) x 0,7 = 0,09 x 0,7 = 0,063
3. 0,05 < 0,09 x 0,7 – (0,020 – 0,017) x 0,76 = 0,061
YES
YES
YES
This is possible, but not very likely due to the low decrease of S.
5. Result is Mgresidual = 0,05 % and Sresidual = 0,012 %
1. 0,012 < 0,020
2. 0,05 < (0,014x0,07/100) x 0,7 = 0,09 x 0,7 = 0,063
3. 0,05 < 0,09 x 0,7 – (0,020 – 0,012) x 0,76 = 0,057
YES
YES
YES
This is possible.
Ir G.D HENDERIECKX
GIETECH BV
OKTOBER 2009
7